New rotary engine from Mazda: technology and perspective

This is the return of the house style: Mazda, always known for unconventional approaches to car technology, has brought the rotary engine into the light of day. The engine, developed by German engineer Felix Wankel and built under license by Mazda since 1967, was further developed to a certain perfection in Japan. And this despite the fact that the basic problems with this technology, including high consumption and poor fuel efficiency compared to reciprocating engines, remained until the end. This conclusion was marked by the Mazda RX-8. It was the last Wankel engine model to be discontinued in 2012.

Ten years later, with the MX-30e-Skyactiv R-EV, Mazda makes it clear that at its headquarters in Fuchū, Japan, the rotary piston concept was only given a creative break. An engine with a triangular rotor celebrates its renaissance. However, it is no longer as a motor itself, but as an electric generator. In conjunction with the downstream generator and electric drive, it serves as a so-called range extender.

New single disc engine

The manufacturer relies on a completely new engine developed for the MX-30, the twelfth model in the history of Mazda with a rotary piston engine. The machine has a room volume of 830 cm³ (hence the local designation as engine type 8C) and produces a maximum output of 55 kW/75 HP. For comparison: the two-disc engine on the last Mazda RX-8 got 2 x 654 cm.³ The volume of the room for a total of 1.3 liters. The compression ratio of the new engine is a high ratio of 11.9:1, and fuel is supplied through direct gasoline injection. This unit meets Euro 6d-ISC-FCM emission standards with exhaust gas distribution, catalytic converter and particulate filter.

Compared to the previous engine type 13B from the RX-8, the new machine uses aluminum instead of cast iron for the side housing. Overall, according to Mazda, the machine is 15 kg lighter than the 13B. And above all, significantly thinner. The rotor is only 76 millimeters wide and the entire motor housing is only 8.4 centimeters wide. This means it can be combined with a generator and an electric machine to create a highly integrated unit.

A motorhome with a width of only 84 mm

Early rotary piston engines had the problem of incomplete combustion of the fuel-air mixture due to the injection technology used at the time. The portion of the mixture above the spark plug was partially released into the exhaust gas without combustion. This problem is said to be eliminated with the new 8C engine with direct petrol injection. According to Mazda, direct injection into the combustion chamber together with a special flow of combustion air that flows through two side inlets ensures the best distribution of the fuel-air mixture in the combustion chamber.

In addition, the compression ratio has been increased to further improve efficiency, it is 11.9: 1. For comparison: The 13B engine type in the Mazda RX-8 had a compression ratio of 9.4: 1. Further improvement measures include new sealing pieces on the rotor, which is wider and causes less frictional losses. In addition, new sealing rings should also have a better service life. In addition, the surfaces of the housings of the side cars were provided with a ceramic coating, which also reduces friction losses.

Low speed, very smooth running

The new rotary piston engine reaches its peak performance quite early; 55 kW/75 hp is 4,700 rpm. A maximum of 116 Nm is available at 4,000 rpm. This shows that the engine, which runs very well because of the system, is not very noticeable inside the car during the operation of the generator. The engine is primarily used as a generator on long trips. As soon as the traction battery capacity drops below 40 percent, the Wankel combustion engine is activated as a power generator. The battery capacity of 17.8 kWh is quite high for a plug-in hybrid and should enable an electric range of up to 85 km.

That still leaves the matter of utility, which hasn’t always been the star specialty of Wankel engines. Mazda does not provide the actual consumption value of the new 8C machine, and the WLTP consumption (1.0l + 17.5 kWh / 100 km) also does not give the slightest indication of the thirst of the engine of 830 cubic centimeters. You can get something out of the top-of-the-range MX-30 with its 55 liter tank. In fact, Mazda specifies this as “more than 600 km”. Theoretically, excluding the excellent electric range, about 515 kilometers remained in generator mode to empty the 55-liter tank with a corresponding consumption of more than ten liters per 100 kilometers.

This is how Mazda continues to promote the Wankel

However, the second job of the Wankel engine at Mazda does not end with its use as a generator in the MX-30 R-EV. In contrast, the Japanese continue to see great potential in technology. The “rotary piston engine development group” established at the beginning of February 2024 and consisting of 36 people is intended to make the Wankel future-proof. The new department is responsible for the further development of generator drive technology in serial hybrid drives. Another area of ​​responsibility is research and development in areas such as regulatory compliance in key markets and CO consumption.₂– neutral oil.